Seismograph and applicable to other measuring instruments



J. H. JONES 1,774,379

SEISMOGRAPH AND APPLICABLE TO OTHER MEASURING INSTRUMENTS Aug. 26, 1930.

Filed Nov. 29, 1929 3 Sheets-Sheet Inventor j/g mw Aug. 26, 1930. J. H.JONES 1,774,379

SEISMOGRAPH AND APPLICABLE TO OTHER MEASURING INSTRUMENTS Filed Nov. 29,1929 5 Sheets-Sheet 2 Fig.6

Inventor flttarney.

6, 1930. J. JONES 1,774,319

SEISMOGRAPH AND APPLICABLE TO OTHER MEASURING INSTRUMENTS Filed Nov. 29,1929 :s sneets lsheet s $1 \c O @F @l Ea o 9;; g a Fig.4. g 9

Inventor Attorney.

Patented Aug. 26, 1930 v UNITED STATES PATENT OFFICE JOHN HUGH JONES, OF

SEISMOGBAPI-I AND APPLICABLE TO Application filed November 29, 1929, SriaI No.

This invention relates to means or indicating or recording smalldisplacements.

According to the invention the small displacements to be magnified areimparted to a magnetic element, for example, to a thin iron strip ofsuitable shape, held suspended in a direction transverse to a rapidlydistorting magnetic field, that is to say, a magnetic field the value ofwhich changes appreciably from point to point, so that the lines ofmagnetic force are strongly curved. The arrangement is such that thesuspended element will take up a position parallel or nearly parallel tothe tangent to the line of force at any particular point, and thus it asmall mirror is attached to the suspended element and the suspendedelement and the source of the field be moved relatively to one anotherthere will be a rotation of the mirror proportional to the displacementof the sus pended element, provided this displacement is small. Thussmall displacements of the suspended element otherwise indiscerniblemaybe indicated or recorded.

The means described may be employed to record small earth movementsimparted to apendulum or seismograph of either the horizontal orvertical type. It may also be employed in connection with a balance, themirror magnifying device described being attached to a spring or otherkind of balance to record minute changes of loading.

It will be understood that the invention is of broad application as ameans for indicating small displacements in the use of a mirror attachedto an element so suspended that it may take up a position parallel ornearly parallel to the tangent to the line of force at any particularpoint, whereby the attached mirror may be rotated on the movementimparted to the suspended element as the result of such smalldisplacements the rotation of the mirror being proportional to thedisplacements or to the currents to be measured or indicated.

The rapidly varying magnetic field may be produced by means of apermanent or other magnet having the north and south poles brought intoproximity to the magnetic element in such manner that at the point whereHASTINGS, ENGLAND OTHER MEASURING INSTRUMENTS 410,435, and inGreatBritain August 9, 1928.

the said element is disposed the lines of magnetic force are stronglycurved. It is, however, preferable for the lield to be produced by meansof two magnets so disposed relatively one to the other that the lines ofmagnetic force in which the element is disposed are stronglyconcentrated and the sensitiveness of the instrument is therebyincreased. The maximum elfect is secured in circumstances whcre therespective fields produced by the two magnets have the same direction.

The application of the invention is illustrated in theaccompanyingdiagrammatic drawings by way of example.

Figure 1 is a view in front elevation of a seismograph provided with amagnetic magnifier according to the invention.

Figure 2 is a side elevation corresponding to Figure 1.

Figure 3 is a plan view of the magnetic magnifier of the seismographshown in Figures 1 and 2 to an enlarged scale.

Figure 4 is a detail plan View of the main slides for the adjustment ofthe magnets of the magnetic magnifier shown in Figures 1 and 2 to anenlarged scale.

Figure 5 is a plan view of the cross slides supporting the magnets inthe said magnetic magnifier also to the enlarged scale.

Figures 6 and 7 are diagrams illustrative of the operation of themagnetic magnifier as applied to an oscillograph.

In carrying the invention into etl'ect in its application to aseismograph provided with a construction of the magnetic magnifier asrepresented in Figures 1 to 5 of the accompanying drawings, a basefitting a is provided to support a standard or pedestal fitting b, whichin turn supports the base plate 0 of the magnetic magnifier having arectangular opening 0 for the passage of the helm or member by which themagnetic element is carried. The base plate 0 is provided with slidewaysc in parallel disposition on opposite sides of the opening 0 for thereception of slides 0 which in turn serve respectively to carry crossslideways c" in which are mounted cross slides a which respectivelysupport the magnets 03 and 6 retained upon the said cross slides byclamping plates 0. The main slides c are adapted to be adjusted byadjusting screws which res )ectively press upon one end of each main slie against the action of a helical spring 0 housed in recesses formedpartly in the slides and partly in the ends of the slideways 0 The crossslides a are similarly adapted for adjustment of position under controlof adjusting screws 0 against the action of springs 0 By such aconstruction the possibility of backlash in the screws is avoided.Similarly, means may be provided to compensate for wear of the holeswithin which the adjusting screws are disposed comprising libre pelletssuch as 0 disposed in horings in the ends of the slideways andn'iaintained in contact with the adjusting screws by means of grubscrews 0".

The magnets 11 and e are conveniently formed of bar metal and ofhorse-shoe shape, while the pole pieces (1, (2 formed of strip metal aremounted upon the ends of the magnets to provide a suitable polar gap ata suitable position in relation to the position to be occupied by themagnetic element. F or this purpose the pole shoes are advantageouslycurved outwardly from the ends of the magnets, and in order to ermit thewidth of the polar gap to be ad usted the shoes are advantageouslymounted upon the ends of the magnets by means of screws passing throughslots disposed in the longitudinal direction of the pole shoes. Thelatter are, moreover, advantageously flanged at the upper edge so thatthe flanges may rest upon the ends of the magnets and thus the positionof the pole shoes may be maintained notwithstanding the adjustmente'liectcd by means of the screws.

The pole shoes of the magnet c are ad vantageously formed for thereception of coils electrically connected up to the terminals c which inturn are connected up to the ter minals c on the base of the instrument.The coils are wouml in the samc direction so that a current may bepassed through the coils in such manner that a modification ol' themagnetic. field produced by the magnet c is secured, both as regards itsintensity and its direction. and so that a distortion of the field maybe etl'ected to secure a determined zero position of the magneticelement. The magnet (Z may similarly be fitted with control coils.

The magnetic element f of the magnifier conveniently comprises a thiniron strip, of a width slightly less than the width of the polar gap,suspended opposite. the polar gaps of the pole shoes (l and betweenthem, and advantageously closer. for example, to the pole shoes 0 thanto the pole shoes (P. A minute mirror 7 is mounted upon the element f soas to be positioned opposite the pole gap of the shoes d to receive abeam of light reflected directly thereon through the said pole gap. Topermit this the rear portion of the magnet rZ is inclined upwardly outof the path of the beam of light and to form a passage through whichsuch beam may be projected. The manner of adjustment of the slidescarrying the magnets hercinbefore described permits of the pole shoes (1and e being adjusted relatively to the ma gnetic element both in adirection transverse to the element and in a dirccton paralleltherewith, so that any desired disposition of the pole shoes may besecured.

The pole gap of the pole shoes 0 is advantageously filled by means of amass of copper which conveniently has secured to it thin plates of amaterial such as mica, cclluloid or the like forming flanges whichextend laterally over the pole shoe faces, and serve to position thecopper mass, while similarly a strip of the material may be secured tothe upper surface of the copper mass so as to rest upon the upper edgesof the pole shoes, and thus to support the mass. Alternatively, a singlestrip of the material may be doubled and secured to the two sides of thecopper mass for the same purpose. The material facing the pole shoesadjacent the magnetic element serves to prevent adhesion of the magneticelement to the pole shoes in the event of an excessive movement.

The base fitting a is advantageously constructed to support the weight gof the seismograph, and for this purpose is provided with an upstandingportion a at the rear, which portion also serves to support the pedestalb and to form the foot thereof. The Weight g is provided with acylindrical case and is carried from the upstanding portion ot'the basea by means of pairs of spring strip metal. one pair being disposed inthe vertical direction and the other pair g in the horizontaldirectioi'i. The. strips g are secured at their upper ends by screws toprojecting faces formed upon the upstanding portion of the base a. andat their lower ends to the faces of corresponding lugs provided upon thecylinder or weight Similarly, the strips 9 are secured at theirrespective ends to lugs formed respectively at the sides of theupstanding portion of the base a and at the ends of the cylinder orweight g. The effective action of the weight g is controlled by means ofa helical spring g which at one end is attached to a downwardlyextending lug 9 provided upon the cylinder or weight g, and at the otherend is attached to a screw-threaded spindle g which passes withclearance through a boring in an upstanding bearing block a and isengaged by an adjusting nut or head a which advantageously bears bymeans of a washer a upon a ball thrust bearing a seated Within thebearing block (1 The adjusting nut or head is advantageously graduatedand co-operates with an index pointer a loo carried by the bearingblock. By the rotation of the said head in the one direction or theother the spindle g is advanced or retracted to increase or decrease thetension of the spring 9 A'lock nut 11 is provided upon the spindle g tomaintain the ad usted position of the head a. In order to permit thebase to be effectively levelled, it is conveniently supported by threescrewed pins a with milled heads, which pins re spectively engagecorresponding supporting lugs extending laterally from opposite sides ofthe base.

In order that the weight g may when desired be maintained in a fixedposition, as when the instrument is under transport, there areconveniently provided two clamping blocks a with chamfered upper faces,which blocks are disposed to slide within a suitable grooved slidewayformed in the base a and are adapted to engage the under-surface of theweight 9 when advanced towards each other by means of a double threadedscrew a which is rotatably carried within an upstanding bearing block aon the base. In addition the pedestal b has advantageously mountedthereon a pressure member 12 adapted to press downwardly upon the weight1 under the action of an adjusting screw 12 mounted in the pedestal b.lVhen it is required to free the weight it is necessary only that thescrew b should be retracted to permit the spring 6 to lift the pressuremember 6 from the weightand that the screw a should be rotated for theseparation of the clamping blocks a".

The weight 9 serves to support a light conical helm h of thin sheetcopper or aluminum, the upper end of which extends through the opening 0of the base plate of the magnetic magnifier. The head of the helm h isfitted with a cap it which is formed with a groove or depression havinga semi-circular surface over which may be led the suspend ing member 71for the magnetic element, the said member 2' being of phosphor-bronzewire or ribbon and being attached to the helm h by means of a transversepin which engages slots in the lower edge of a U-shaped fitting kmounted upon the helm and led upwardly over a bridge fitting if over thecap k successivelyover bridge fittings k and it also provided upon thehelm, in engagement with a hook it, and connected at its lower end to ahelical spring 7' connected in turn to a screw-threaded pin which passesthrough a hole in a transversely disposed flange of a bracket g fittedupon the weight 9 adjacent the base of the cone or helm k. The magneticelement 7 carrying the mirror 7' is mounted upon the member 2' at aposition between the bridges h and if.

The cone or helm h is conveniently mounted around a circular seatingprovided upon the weight g to which it may be secured by a split ringengaged by a clamping screw and nut.

An enclosing casing is is advantageously provided to enclose the wholeof the instrument, such casing fitting around the base a and beingsecured thereto by suitable means, as by screws. The upper part of thecasing is conveniently provided as a hood 7: hinged to the main body ofthe casing so that it may be readily thrown back to expose the magneticmagnifier. The two parts of the casing may be provided at the meetingedges with angle metal to add strength and to form suitable contactingsurfaces. A suitable fastening k may be provided at the opposite side tothe hinge connecting the. two parts of the casing. The hood 7.: isformed with an aperture or window lr" at a. suitable position to permit.the direction of a beam of light from a suitable source into the casingand against the mirror P.

It will be understood that in the operation of the instrument, when thema netic element is moved in the magnetic held as the result ofthe'vibrations of the helm, the element will set itself tangential tothe lines of force and in so doing will partially rotate and cause themirror to deflect a beam of light directed upon it in such manner thatthe displacement of the element due to the vibration of the helm may beobserved or recorded, in any suitable manner, as for example, by thedirection of the reflected beam on to a moving sensitive surface.

It will be understood that the vibration may if desired be imparted tothe magnetic system rather than to the magnetic element, while, furtherthe manner in which the magnetic system is mounted and adjusted inrelation to the element is immaterial to the invention.

In the application of the magnetic system, as indicated by the diagramsFigures (3 and 7, a current flowing through the coils weakens one poleand strengthens the other pole. The effect of the current is thereforeto distort the magnetic field in the manner that is indicated by fulllines in the diagram, Figure 7. Upon the reversal of the current,however, the field is distorted in the manner that is indicated by thebroken lines in Figure 6. Thus, considering a point A, as in Figure 7,the magnetic field of the magnet normally is in a direction parallelwith the pole pieces. The effect of the weakening of the magnetism ofone pole and the strengthening of the magnetism of the other pole causesthe resultant field at the point A to be inclined in the direction ofthe diagonal of the parallelogram of forces there illustrated. ()n thereversal of the current the diagonal will be inclined on the oppositeside of the normal direction of the field. Thus, when the nar rowmagnetic element is set at the point A in the rapidly distorted magneticfield, it will tend to set, itsell' to follow the periodically changingdirections of inclination of the magnetic tichl with respect. to itsnormal position and will thus oscillate. through a correspondiug smallangle. mirror attached thereto will therel'ore retlect a beam of lightand record the variat ions of the current when directed upon a movingsensitive surface.

It will l'urther he understood that the inanner in which the magneticmagnifier is applied is capable of variation without departing from theinvention, and that it may be utilized in various types of seismographs,oseillographs and other measuring instruments.

I claim 1. In a recording seismograph or like. recording instrument, aplurality of magnets set in two opposed positions to produce a rapidlyvarying intense magnetic field having strongly curved lines of force, amagnetic element disposed between the magnets in the said magnetic fieldso as to take up a position approximately parallel to the tangent to thelines of force at that position, electrical means for rapidly distortingthe magnetic field periodically and alternately in opposite directions,a vibratory member from which the magnetic element is freely suspended,the said vibratory element having imparted to it the displacements to beindicated, and a mirror carried by the magnetic element.

21111 a recording seismograph or like recording instrument, two magnetsset in opposed positions and serving to produce a rapidly varyingintense magnetic field having strongly curved lines of force, one ofsaid magnets being provided with electrical coils for rapidly distortingthe magnetic field produced thereby periodically and alternately inopposite directions, a magnetic element free- 1y suspended between thesaid magnets in the said field to occupy a position approximatelyparallel to the tangent to the lines of force at the particularposition, means for adjusting the magnets relatively one to the otherand in relation to the magnetic element, a vibratory member to which thedisplacements to be indicated are imparted and from which the magneticelement is freely suspended, and a mirror carried by the said magneticelement.

3. In a recording seismograph or like recording instrument, a magneticsystem producing a rapidly varying intense magnetic field havingstrongly curved lines of force, a support in fixed relation to saidmagnetic system, a weight carried by said support in such manner as tobe free to vibrate, a vibratory member extending from the said weightinto the said magnetic field, a magnetic element freely suspended uponthe said vibratory member in such manner that it may take up a positionapproximately parallel to the lines of force at the particular position,electrical means for rapidly distorting the magnetic field periodicallyand alternately at an angle in opposite directions, means for adjustingthe etl'ective action of the weight, and a mirror carried by themagnetic element.

4. In a recording seismograph or like recording instrument, a magneticsystem producing a rapidly varying intense magnetic field havingstrongly curved lines of force, a support in fixed relation to saidmagnetic system, a weight carried by said support in such manner as tohe tree to vibrate, a vibratory member extending from the said weightinto the said magnetic field, a magnetic element 'l'recly suspended uponthe said vibratory member in such manner that it may take up a positionapproximately parallel to the lines of force at the particular position,electrical means for rapidly distorting the magnetic field periodicallyand alternately at an angle in opposite directions, and a mirror carriedby the magnetic element.

JOHN HUGH JONES.

